I'd say a healthy metagame isn't too over centralized on one Pokemon or a certain move(s) like Priority Moves + Knoff Off, while being as balanced as possible. Some pokemon in like Aurorus need to have their completely rearranged stats to be viable in their own tier.
Currently, the official meta is VGC, but, many go the Smogon route. Smogon's rules are almost perfect, but, sometimes, good and fair play styles are bad while others aren't.
What I'd like in Gen 7 is that Knock-off gets a slight nerf, a move/ability that reverses all priority and Rock, Ice and Grass gets a buff.
Mega Kangaskhan's Parental Bond should be nerfed to inflict only 15% damage the second time it hits and hopeful, M-Lopunny can bring Mega-Gengar from it's throne
Other than that, OU is okayish while the other tiers are close to god-like invariation.
